diff --git a/src/config/env.rs b/src/config/env.rs
index 0ab221d1..6ad8e56c 100644
--- a/src/config/env.rs
+++ b/src/config/env.rs
@@ -5,10 +5,12 @@
 
 mod catalog;
 pub mod dump;
+pub mod joinir_dev;
 pub mod stage1;
 
 pub use catalog::{env_vars, AppliesTo, EnvVarMeta};
 pub use dump::*;
+pub use joinir_dev::*;
 pub use stage1::*;
 use std::collections::BTreeMap;
 
diff --git a/src/config/env/joinir_dev.rs b/src/config/env/joinir_dev.rs
new file mode 100644
index 00000000..e5164fd8
--- /dev/null
+++ b/src/config/env/joinir_dev.rs
@@ -0,0 +1,50 @@
+//! JoinIR development / experimental flags (SSOT).
+//! Phase 72-C: Consolidate all NYASH_JOINIR_* dev flags through centralized helpers.
+
+use crate::config::env::env_bool;
+
+/// NYASH_JOINIR_LOWER_GENERIC=1 - Enable generic lowering path for JoinIR
+/// (CRITICAL: 15 occurrences in codebase)
+pub fn lower_generic_enabled() -> bool {
+    env_bool("NYASH_JOINIR_LOWER_GENERIC")
+}
+
+/// NYASH_JOINIR_MAINLINE_DEBUG=1 - Debug output for mainline JoinIR lowering
+pub fn mainline_debug_enabled() -> bool {
+    env_bool("NYASH_JOINIR_MAINLINE_DEBUG")
+}
+
+/// NYASH_JOINIR_IF_MERGE=1 - Enable If-merge experimental mode
+pub fn if_merge_enabled() -> bool {
+    env_bool("NYASH_JOINIR_IF_MERGE")
+}
+
+/// NYASH_JOINIR_DEBUG=1 - General debug mode (deprecated, prefer mainline_debug)
+pub fn debug_enabled() -> bool {
+    env_bool("NYASH_JOINIR_DEBUG")
+}
+
+/// NYASH_JOINIR_VM_BRIDGE=1 - Enable VM bridge mode
+pub fn vm_bridge_enabled() -> bool {
+    env_bool("NYASH_JOINIR_VM_BRIDGE")
+}
+
+/// NYASH_JOINIR_STRICT=1 - Strict validation mode
+pub fn strict_enabled() -> bool {
+    env_bool("NYASH_JOINIR_STRICT")
+}
+
+/// NYASH_JOINIR_SNAPSHOT_GENERATE=1 - Generate snapshot for testing
+pub fn snapshot_generate_enabled() -> bool {
+    env_bool("NYASH_JOINIR_SNAPSHOT_GENERATE")
+}
+
+/// NYASH_JOINIR_SNAPSHOT_TEST=1 - Test using snapshot
+pub fn snapshot_test_enabled() -> bool {
+    env_bool("NYASH_JOINIR_SNAPSHOT_TEST")
+}
+
+/// NYASH_JOINIR_INPUT=* - Input source or mode
+pub fn input_mode() -> Option<String> {
+    std::env::var("NYASH_JOINIR_INPUT").ok()
+}